1. Field of the Invention
The present invention relates to a mobile communication system, a wireless base station and a hand over reconnection method for use therewith, and more particularly to a hand over reconnection method without data loss in a third generation mobile communication system that is standardized by a standardization organization (3GPP: 3rd Generation Partnership Project).
2. Description of the Related Art
In the Release 7 of the 3GPP, as an evolved UTRAN [UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network], a network in which a wireless base station (NodeB) and a radio network controller (RNC: Radio Network Controller) are integrated is supposed and examined. In the following, an apparatus in which the wireless base station and the radio network controller are integrated is an integrated wireless base station (eNodeB: evolved UTRAN NodeB).
In a hand over procedure for the integrated wireless base station, a method for transferring the user data from one integrated wireless base station to another to prevent the loss of user data is resolved (e.g., refer to non-patent document 1 (“3rd Generation Partnership Project: Technical Specification Group Radio Access Network; Evolved UTRA and UTRAN; Radio Access Architecture and Interfaces (Release 7) 6.3.3.2.2 Option U-2) Forwarding Source eNodeB→Target eNodeB” [3GPP TR R3.018 V0.2.1 (2006-04)]).
However, since a delivery confirmation for user data is not made between the integrated wireless base stations, if the hand over fails due to a radio error halfway during the hand over procedure, a data loss occurs. In an NRT (Non Real Time) service, especially when a large volume of data is downloaded, it is required to retransmit the data from the beginning or perform a retransmission process on a TCP (Transmission Control Protocol) layer, if there is a data loss even though a reconnection process is successful, so that a large load is imposed on the radio network.
Accordingly, in the NRT service, though some delay is permitted, it is preferable that the data loss is as small as possible. Even if the hand over fails, especially in passing through a tunnel while moving at high speed, the communication can be resumed without loss of user data if the reconnection process is successful after passing through the tunnel.
In the hand over procedure at the wireless base station, the methods for buffering the user data to mobile terminal equipment at the wireless base station have been proposed (e.g., refer to patent documents 1-3 (Japanese patent application No. 2003-283510, Japanese patent application No. 2004-304325, and Japanese patent application No. 2005-287074)). With these methods, since the delivery confirmation for user data is not made, data is lost if the hand over fails due to a radio error halfway during the hand over procedure.
In the hand over procedure for the integrated wireless base station examined by the 3GPP, it is decided that the user data is transferred from one integrated wireless base station to another to prevent the loss of user data. However, since the delivery confirmation for user data is not made between the integrated wireless base stations, data is lost if the hand over fails due to a radio error halfway during the hand over procedure.
In an NRT service, especially when a large amount of data is downloaded, it is required to retransmit the data from the beginning or perform a retransmission process on the TCP layer, when there is a data loss even though a reconnection process is successful, so that a large load is imposed on the radio network. Accordingly, it is considered that some delay is permitted in the NRT service but the data loss is preferably as small as possible.